JP2017091820A - Negative electrode active material for electric device, and electric device arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means which enables the enhancement in the cycle durability of an electric device, such as a lithium ion secondary battery.SOLUTION: A silicon-containing alloy is used as a negative electrode active material for an electric device, which comprises a ternary alloy composition expressed by Si-Sn-M (where M represents one or more transition metal elements). The silicon-containing alloy has a structure in which a-Si phases including amorphous or low-crystallinity silicon and formed as a result of solid dissolution of tin in a silicon crystal structure are dispersed in a silicide phase including a transition metal silicide as a primary component. With the a-Si phases, the inter-Si tetrahedron distance is 0.38 nm or more according to TEM-MRO analysis. In X-ray diffraction measurement with CuKα1 rays, the ratio (B/A) of a diffraction peak intensity B of (311) plane of the transition metal silicide in a range of 2θ=37-45° to a diffraction peak intensity A of Si (111) plane in a range of 2θ=24-33° is 1.34 or larger.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a negative electrode active material for electric devices and an electric device using the same. The negative electrode active material for an electric device and the electric device using the same according to the present invention include, for example, a driving power source and an auxiliary power source for a motor of a vehicle such as an electric vehicle, a fuel cell vehicle, and a hybrid electric vehicle as a secondary battery or a capacitor. Used for

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electric devices such as secondary batteries for motor drive that hold the key to their practical application. Is being actively developed.

  As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in a mobile phone, a notebook personal computer or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

Conventionally, carbon / graphite-based materials that are advantageous in terms of charge / discharge cycle life and cost have been used for negative electrodes of lithium ion secondary batteries. However, since carbon / graphite-based negative electrode materials are charged / discharged by occlusion / release of lithium ions into / from graphite crystals, the charge / discharge capacity of the theoretical capacity 372 mAh / g or more obtained from LiC ₆ which is the maximum lithium-introduced compound. There is a disadvantage that cannot be obtained. For this reason, it is difficult to obtain a capacity and energy density that satisfy the practical use level of the vehicle application with the carbon / graphite negative electrode material.

On the other hand, a battery using a material that is alloyed with Li for the negative electrode is expected as a negative electrode material for vehicle use because the energy density is improved as compared with a conventional carbon / graphite negative electrode material. For example, the Si material occludes and releases _3.75 mol of lithium ions per mol as shown in the following reaction formula (A) in charge / discharge, and the theoretical capacity is 3600 mAh / liter in Li ₁₅ Si ₄ (= Li _3.75 Si). g.

  However, a lithium ion secondary battery using a material that is alloyed with Li for the negative electrode has a large expansion and contraction in the negative electrode during charge and discharge. For example, when Li ions are occluded, the volume expansion is about 1.2 times in graphite materials, whereas in Si materials, when Si and Li are alloyed, transition from the amorphous state to the crystalline state causes a large volume change. (Approximately 4 times), there was a problem of reducing the cycle life of the electrode. In the case of the Si negative electrode active material, the capacity and the cycle durability are in a trade-off relationship, and there is a problem that it is difficult to improve the cycle durability while exhibiting a high capacity.

Here, Patent Document 1 discloses an invention that aims to provide a non-aqueous electrolyte secondary battery having a negative electrode pellet having a high capacity and an excellent cycle life. Specifically, a silicon-containing alloy obtained by mixing silicon powder and titanium powder by a mechanical alloying method and wet-pulverizing the first phase mainly composed of silicon and a silicide of titanium (such as TiSi ₂ ) ) Containing a second phase containing) is disclosed as a negative electrode active material. At this time, it is also disclosed that at least one of these two phases is amorphous or low crystalline.

International Publication No. 2006/129415 Pamphlet

  According to the study by the present inventors, although it is said that the electric device such as a lithium ion secondary battery using the negative electrode pellet described in Patent Document 1 can exhibit good cycle durability. Therefore, it has been found that the cycle durability may not be sufficient.

  Then, an object of this invention is to provide the means which can improve the cycling durability of electric devices, such as a lithium ion secondary battery.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, it has a ternary alloy composition represented by Si-Sn-M (M is one or more transition metal elements), and tin is solid-solved inside the silicon crystal structure. A silicon-containing alloy having a structure in which an a-Si phase containing amorphous or low crystalline silicon is dispersed in a silicide phase mainly composed of a transition metal silicide is used as a negative electrode active material for an electric device. In addition, the present inventors have found that the above problem can be solved by controlling the distance between Si tetrahedrons in the silicon-containing alloy and the value of the silicide / Si peak intensity ratio by X-ray diffraction measurement, and completed the present invention. It was.

That is, this invention relates to the negative electrode active material for electric devices which consists of a silicon containing alloy. And the said silicon containing alloy has the characteristics in the point which satisfy | fills the prescription | regulation of following (A)-(D):
(A) The following chemical formula (I):

(In the above chemical formula (I),
A is an inevitable impurity,
M is one or more transition metal elements,
x, y, z, and a represent mass% values, where 0 <x <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100. )
Having a composition represented by:
(B) The a-Si phase containing amorphous or low crystalline silicon in which tin is dissolved in the silicon crystal structure is dispersed in a silicide phase mainly composed of a transition metal silicide. Having a structure of
(C) The Si tetrahedral distance by TEM-MRO analysis for the a-Si phase is 0.38 nm or more;
(D) In the X-ray diffraction measurement using CuKα1 line, the transition metal silicide in the range of 2θ = 37 to 45 ° with respect to the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 ° The value (B / A) of the diffraction peak intensity B of the (311) plane is 1.34 or more.

The silicon-containing alloy constituting the negative electrode active material according to the present invention has a ternary alloy composition represented by Si-Sn-M (M is one or more transition metal elements), It has a structure in which an a-Si phase containing amorphous or low crystalline silicon in which tin is dissolved in a crystal structure is dispersed in a silicide phase mainly composed of a transition metal silicide. However, it contributes to the realization of high cycle durability. That is, in this way, when the silicide phase constitutes a sea (continuous phase) having a sea-island structure, the electron conductivity of the negative electrode active material (silicon-containing alloy) can be further improved, and the a-Si phase It is possible to relieve stress during expansion and prevent cracking of the active material. In addition, when the distance between Si tetrahedrons in the amorphous region (a-Si phase) is a value greater than or equal to a predetermined value, the insertion / extraction reaction of lithium ions during charge / discharge easily proceeds. it is conceivable that. Furthermore, when the SiM / Si peak intensity ratio (B / A) is a value equal to or greater than a predetermined value, the amorphous-crystal phase transition (to Li ₁₅ Si ₄₎ when Si and Li are alloyed during charging. It is considered that this leads to relaxation of the expansion of the active material particles during charging / discharging while suppressing crystallization of the active material particles. As a result of these combined actions, the negative electrode active material according to the present invention provides improved cycle durability of the electrical device.

FIG. 1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of an electric device according to the present invention. FIG. 2 is a perspective view schematically showing the appearance of a stacked flat lithium ion secondary battery which is a typical embodiment of the electric device according to the present invention. FIG. 3 is a photograph showing the results of observation of the negative electrode active material (silicon-containing alloy) of Example 1 by HAADF-STEM. FIG. 3A is an image obtained by performing element strength mapping by EDX on an observation image (low magnification) of the negative electrode active material (silicon-containing alloy) of Example 1 by HAADF-STEM. FIG. 3B is a photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of Example 1 shown in FIG. FIG. 4 is an image obtained by performing element strength mapping by EDX on observation images (low magnification) of Examples 3 to 5 and comparative example negative electrode active materials (silicon-containing alloys) by HAADF-STEM. 4 (A): Example 3, FIG. 4 (B): Example 4, FIG. 4 (C): Example 5, FIG. 4 (D): Comparative example. FIG. 5 is a photograph for explaining a method of measuring the distance between Si tetrahedrons in the amorphous region (a-Si phase) of the negative electrode active material (silicon-containing alloy) of Example 1. Specifically, FIG. 5A is an enlarged photograph of a lattice image obtained by HAADF-STEM of the negative electrode active material (silicon-containing alloy) of Example 1. FIG. 5B shows a diffraction pattern obtained by performing a fast Fourier transform (FFT) process on the lattice image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. It is a photograph shown. FIG. 5C shows an inverse Fourier transform obtained by performing inverse fast Fourier transform processing on the extracted figure from which data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 5B is extracted. It is a photograph which shows a conversion image. FIG. 6A shows an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) shown in FIG. 4 for the negative electrode active material (silicon-containing alloy) of Examples 3 to 4. It is a photograph which shows a photograph and the inverse Fourier transform image obtained from the said observation image. Specifically, FIG. 6A (A) is a photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of Example 3 shown in FIG. 4 (A). FIG. 6A (B) is an inverse Fourier transform image of Example 3 obtained from the observation image of FIG. 6A (A). Similarly, FIG. 6A (C) is a photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of Example 4 shown in FIG. 4 (B). 6A (D) is an inverse Fourier transform image of Example 4 obtained from the observation image of FIG. 6A (C). 6B is an observation image (high magnification) obtained by enlarging the portion surrounded by the square of the HAADF-STEM observation image (low magnification) shown in FIG. 4 for the negative electrode active material (silicon-containing alloy) of Example 5 and Comparative Example. It is the photograph which shows the photograph which shows, and the inverse Fourier transform image obtained from the said observation image. Specifically, FIG. 6B (E) is a photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of Example 5 shown in FIG. 4 (C). FIG. 6B (F) is an inverse Fourier transform image of Example 5 obtained from the observation image of FIG. 6B (E). Similarly, FIG. 6B (G) is a photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of the comparative example shown in FIG. 4 (D). FIG. 6B (H) is an inverse Fourier transform image of a comparative example obtained from the observation image of FIG. 6B (G). FIG. 7A shows an observation image (HAADF-STEM image) obtained by observing the microstructure of the negative electrode active material (silicon-containing alloy) of Example 1 with HAADF-STEM, an enlarged image thereof, and a black portion (a -Si phase) and gray portions of the area of (silicide (TiSi ₂₎ phase) is a photograph showing a diffraction pattern obtained by fast Fourier transform. FIG. 7B shows an observation image (HAADF-STEM image) obtained by observing the microstructure of the negative electrode active material (silicon-containing alloy) of Example 3 with HAADF-STEM, an enlarged image thereof, and a black portion (a -Si phase) and gray portions of the area of (silicide (TiSi ₂₎ phase) is a photograph showing a diffraction pattern obtained by fast Fourier transform. FIG. 7C shows an observation image (HAADF-STEM image) obtained by observing the microstructure of the negative electrode active material (silicon-containing alloy) of Example 4 with HAADF-STEM, an enlarged image thereof, and a black portion (a -Si phase) and gray portions of the area of (silicide (TiSi ₂₎ phase) is a photograph showing a diffraction pattern obtained by fast Fourier transform. FIG. 7D shows an observation image (HAADF-STEM image) obtained by observing the microstructure of the negative electrode active material (silicon-containing alloy) of Example 5 with HAADF-STEM, an enlarged image thereof, and a black portion (a -Si phase) and gray portions of the area of (silicide (TiSi ₂₎ phase) is a photograph showing a diffraction pattern obtained by fast Fourier transform. FIG. 7E shows an observation image (HAADF-STEM image) obtained by observing the microstructure of the negative electrode active material (silicon-containing alloy) of the comparative example with HAADF-STEM, an enlarged image thereof, and a black portion (a- Si phase) and gray portions of the area of (silicide (TiSi ₂₎ phase) is a photograph showing a diffraction pattern obtained by fast Fourier transform. FIG. 7F is an XRD chart for the negative electrode active materials (silicon-containing alloys) of Examples 1 and 3 to 5 and the comparative example.

  Hereinafter, embodiments of a negative electrode active material for an electric device of the present invention and an electric device using the same will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following modes. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  Hereinafter, a basic configuration of an electric device to which the negative electrode active material for an electric device of the present invention can be applied will be described with reference to the drawings. In the present embodiment, a lithium ion secondary battery will be described as an example of an electric device.

  First, in a negative electrode for a lithium ion secondary battery, which is a typical embodiment of a negative electrode including a negative electrode active material for an electric device according to the present invention, and a lithium ion secondary battery using the same, a cell (single cell layer) ) Voltage is large, and high energy density and high power density can be achieved. Therefore, the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment is excellent as a vehicle driving power source or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for a vehicle driving power source or the like. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

  That is, the lithium ion secondary battery that is the subject of the present embodiment may be any one that uses the negative electrode active material for the lithium ion secondary battery of the present embodiment described below. It should not be restricted in particular.

  For example, when the lithium ion secondary battery is distinguished by form / structure, it can be applied to any conventionally known form / structure such as a stacked (flat) battery or a wound (cylindrical) battery. Is. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

  When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a solution electrolyte type battery using a solution electrolyte such as a nonaqueous electrolyte solution for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer, etc. It can be applied to any conventionally known electrolyte layer type. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as polymer electrolyte). It is done.

  Therefore, in the following description, the non-bipolar (internal parallel connection type) lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of this embodiment will be described very simply with reference to the drawings. However, the technical scope of the lithium ion secondary battery of the present embodiment should not be limited to these.

<Overall battery structure>
FIG. 1 schematically shows the overall structure of a flat (stacked) lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”), which is a typical embodiment of the electrical device of the present invention. FIG.

  As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. . Here, in the power generation element 21, the positive electrode in which the positive electrode active material layer 15 is disposed on both surfaces of the positive electrode current collector 12, the electrolyte layer 17, and the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. It has a configuration in which a negative electrode is laminated. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. The positive electrode current collector 15 located on both outermost layers of the power generation element 21 has the positive electrode active material layer 15 disposed only on one side, but the active material layers may be provided on both sides. . That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost negative electrode current collector is positioned on both outermost layers of the power generation element 21, and one side of the outermost negative electrode current collector or A negative electrode active material layer may be disposed on both sides.

  The positive electrode current collector 12 and the negative electrode current collector 11 are attached to the positive electrode current collector plate 27 and the negative electrode current collector plate 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between the end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via a positive electrode lead and a negative electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  The lithium ion secondary battery described above is characterized by a negative electrode. Hereinafter, main components of the battery including the negative electrode will be described.

<Active material layer>
The active material layer 13 or 15 contains an active material, and further contains other additives as necessary.

[Positive electrode active material layer]
The positive electrode active material layer 15 includes a positive electrode active material.

(Positive electrode active material)
Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-such as those obtained by replacing some of these transition metals with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used, and more preferably Li (Ni-Mn-Co) O ₂ and a part of these transition metals substituted with other elements (hereinafter, Simply referred to as “NMC composite oxide”). The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc. that have been proven in general consumer batteries. Compared to the above, the capacity per unit weight is large, and the energy density can be improved, so that a battery having a compact and high capacity can be produced, which is preferable from the viewpoint of cruising distance. In addition, LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in terms of a larger capacity, but there are difficulties in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has life characteristics as excellent as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

  In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. Of course, positive electrode active materials other than those described above may be used.

  The average particle diameter of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but is preferably 1 to 30 μm, more preferably 5 to 20 μm from the viewpoint of increasing the output. In the present specification, the “particle diameter” refers to the outline of the active material particles (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among any two points. In this specification, the value of “average particle diameter” is the value of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle diameter shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner.

  The positive electrode active material layer 15 can include a binder.

(Binder)
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene Copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene Fluororesin such as copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine Rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-teto Fluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene Vinylidene fluoride-based fluororubbers such as epoxy-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1-10 mass%.

  The positive electrode (positive electrode active material layer) can be applied by any one of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method in addition to a method of applying (coating) a normal slurry. Can be formed.

[Negative electrode active material layer]
The negative electrode active material layer 13 includes a negative electrode active material.

(Negative electrode active material)
In the present embodiment, the negative electrode active material is made of a silicon-containing alloy. Hereinafter, although the composition, structure, and physical properties of the silicon-containing alloy according to this embodiment will be described, the silicon-containing alloy according to this embodiment satisfies the following provisions (A) to (D). It is essential that the requirements (E) and (F) be satisfied.

  The silicon-containing alloy constituting the negative electrode active material in the present embodiment first has a ternary alloy composition represented by Si—Sn-M (M is one or more transition metal elements). Yes. More specifically, the silicon-containing alloy constituting the negative electrode active material in the present embodiment has a composition represented by the following chemical formula (I) (regulation (A)).

  In the above chemical formula (I), A is an inevitable impurity, M is one or more transition metal elements, and x, y, z, and a represent mass% values, where 0 <X <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100.

As apparent from the chemical formula (I), the silicon-containing alloy (having the composition of Si _x Sn _y M _z A _a ) according to the present embodiment is a ternary system of Si, Sn, and M (transition metal). is there. By having such a composition, high cycle durability can be realized. Further, in the present specification, the “inevitable impurities” means an Si-containing alloy that exists in a raw material or is inevitably mixed in a manufacturing process. The inevitable impurities are originally unnecessary impurities, but are a very small amount and do not affect the characteristics of the Si alloy.

  In the present embodiment, particularly preferably, Ti is selected as an additive element (M; transition metal) to the negative electrode active material (silicon-containing alloy) to suppress amorphous-crystal phase transition during Li alloying. Cycle life can be improved. This also increases the capacity of conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Therefore, according to a preferred embodiment of the present invention, in the composition represented by the chemical formula (I), M is preferably titanium (Ti).

  Here, in the Si-based negative electrode active material, when Si and Li are alloyed during charging, the Si phase transitions from the amorphous state to the crystalline state, causing a large volume change (about 4 times). As a result, there is a problem that the active material particles themselves are broken and the function as the active material is lost. For this reason, by suppressing the phase transition of the Si-phase amorphous-crystal during charging, the particle itself can be prevented from collapsing, the function (high capacity) as an active material is maintained, and the cycle life is also improved. Can do.

As described above, the silicon-containing alloy according to this embodiment (having the composition of Si _x Sn _y M _z A _a ) is a ternary system of Si, Sn, and M (transition metal). Here, the sum of the constituent ratios (mass ratios x, y, z) of the constituent elements is 100% by mass, but there is no particular limitation on the values of x, y, z. x is preferably 60 ≦ x ≦ 73, more preferably 60 ≦ x ≦ 70, from the viewpoint of maintaining durability against charge / discharge (insertion / desorption of Li ions) and the balance of initial capacity, Preferably 60 ≦ x ≦ 65. In addition, y is dissolved in the Si phase, and by increasing the distance between Si tetrahedrons in the Si phase, from the viewpoint of enabling reversible insertion and desorption of Li ions during charge and discharge, Preferably 2 ≦ y ≦ 15, more preferably 2 ≦ y ≦ 10, and further preferably 5 ≦ y ≦ 10. Z is preferably 25 ≦ z ≦ 35, more preferably 27 ≦ z, from the viewpoint of maintaining durability against charge / discharge (insertion / desorption of Li ions) and balancing the initial capacity, similarly to x. ≦ 33, more preferably 28 ≦ z ≦ 30. Thus, it becomes easy to achieve the microstructure of the silicon-containing alloy according to the present embodiment by containing a relatively large amount of Ti while containing Si as a main component and also including Sn to some extent. However, the numerical ranges of the constituent ratios of the constituent elements described above are merely for explaining preferred embodiments, and are within the technical scope of the present invention as long as they are included in the claims.

  As described above, A is an impurity (unavoidable impurity) other than the three components derived from the raw materials and the manufacturing method. The a is 0 ≦ a <0.5, and preferably 0 ≦ a <0.1. Whether or not the negative electrode active material (silicon-containing alloy) has the composition of the above chemical formula (I) is confirmed by qualitative analysis by fluorescent X-ray analysis (XRF) and quantitative analysis by inductively coupled plasma (ICP) emission spectroscopy. Is possible.

  Subsequently, the silicon-containing alloy constituting the negative electrode active material in the present embodiment is also characterized in that it has a structure in which an a-Si phase is dispersed in a silicide phase (regulation (B)). That is, the feature of the silicon-containing alloy according to the present embodiment is that it has a so-called sea-island structure in which islands composed of a-Si phases as dispersed phases are dispersed in a sea composed of silicide phases as continuous phases. One. Whether or not the silicon-containing alloy has such a microstructure is determined by, for example, using a high-angle annular dark-field scanning transmission electron microscope (see FIG. After observing using HAADF-STEM), the same visual field as the observed image can be confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy).

<A-Si phase>
Here, in the silicon-containing alloy according to the present embodiment, the a-Si phase is a phase containing amorphous or low crystalline silicon in which tin is dissolved in the crystal structure of silicon. This a-Si phase is a phase involved in occlusion / release of lithium ions during operation of the electrical device (lithium ion secondary battery) of the present embodiment, and can electrochemically react with lithium (that is, per weight and This is a phase in which a large amount of lithium can be occluded and released per volume. In addition, although tin is dissolved in the crystal structure of silicon constituting the a-Si phase, since silicon is poor in electron conductivity, a small amount of additive elements such as phosphorus and boron are included in the parent phase. Transition metals and the like may be included. Although there is no restriction | limiting in particular about the size of an a-Si phase, From a viewpoint of suppressing the expansion | swelling at the time of charge, the size of an a-Si phase is so preferable that it is small, specifically, it is preferable that it is 10 nm or less, and is 8 nm or less. More preferably. On the other hand, the lower limit of the size of the a-Si phase is not particularly limited, but is preferably 1 nm or more, more preferably 2 nm or more, still more preferably 5 nm or more, and particularly preferably 8 nm or more. As for the diameter value of the a-Si phase, high magnification (25 nm scale bar) Si EDX element mapping and M (for example, Ti) EDX element mapping in HAADF-STEM are compared, and Si exists. The region where M does not exist is regarded as the Si phase, the intensity is 1/10 of the maximum value in the EDX element mapping of M, and the binarized image processing is performed on the region where the intensity is less than this threshold. From the image, it can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by a method of reading the dimensions of each Si phase. Similarly, with regard to the value of the diameter of the silicide phase described later, high-magnification (25 nm scale bar) Si EDX element mapping and M (for example, Ti) EDX element mapping in Cs-STEM are compared, and Si exists. A region where M also exists is regarded as a silicide phase, and the intensity is 1/10 of the maximum value in the EDX element mapping of M, and binarized image processing is performed for a region where the intensity is greater than or equal to this threshold value. From the converted image, it can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by a method of reading the dimensions of each silicide phase.

  The a-Si phase is preferably made amorphousr than a silicide phase described later. With such a configuration, the negative electrode active material (silicon-containing alloy) can have a higher capacity. Whether or not the a-Si phase is more amorphous than the silicide phase is determined based on observation images of the a-Si phase and the silicide phase using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It can be determined from a diffraction pattern obtained by fast Fourier transform (FFT). That is, the diffraction pattern shown in this diffraction pattern shows a two-dimensional dot array net pattern (lattice spot) for a single crystal phase, a Debye-Scherrer ring (diffraction ring) for a polycrystalline phase, and an amorphous The temperate phase shows a halo pattern. By using this, the above confirmation can be performed. In the present embodiment, the a-Si phase may be amorphous or low crystalline, but the a-Si phase is amorphous from the viewpoint of realizing higher cycle durability. Is preferred.

  In addition, although the silicon-containing alloy which concerns on this embodiment contains tin essential, since tin is an element which does not form a silicide between silicon, it exists in an a-Si phase instead of a silicide phase. And when there is little content of tin, all the tin elements exist in solid solution inside the crystal structure of silicon in the a-Si phase. On the other hand, when the content of tin increases, the tin element that can no longer be dissolved in the silicon of the a-Si phase aggregates and exists as a crystalline phase of simple tin. In this embodiment, it is preferable that such a crystalline phase of simple tin does not exist.

  Moreover, in this embodiment, the range of the distance between Si tetrahedrons about an a-Si phase is also prescribed | regulated. Specifically, it is essential that the distance between Si tetrahedrons for the a-Si phase is 0.38 nm or more (regulation (C)). Here, the value of the distance between Si tetrahedrons for the a-Si phase is measured by the following TEM-MRO analysis (the same measurement was performed for the examples described later).

(Measurement of distance between Si tetrahedrons of a-Si phase by TEM-MRO analysis)
In this measurement, a diffraction pattern is obtained by performing a Fourier transform process from a lattice image obtained by a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) of a silicon-containing alloy. In this diffraction pattern, when the distance between Si tetrahedrons was set to 1.0, an inverse Fourier transform process was performed on a diffraction ring portion existing in a width of 0.7 to 1.0. From the inverse Fourier transform image, it is possible to measure the distance between the Si tetrahedrons while paying attention to the periodic array.

-Lattice image by HAADF-STEM observation Here, observation using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) can be usually performed using HAADF-STEM and a computer. For observation by HAADF-STEM, a method of observing (monitoring) with a computer by enlarging a lattice image (interference image) created by electrons transmitted through the sample to be observed by applying an electron beam to the sample to be observed can be used. According to a transmission electron microscope (TEM), it is possible to obtain a high-resolution observation image enlarged to the atomic level and having high contrast. For example, FIG. 5A is an enlarged photograph of a lattice image obtained by HAADF-STEM of the silicon-containing alloy of this embodiment (specifically, the one prepared in Example 1).

  Next, a Fourier transform process is performed from the lattice image obtained by HAADF-STEM to obtain a diffraction pattern. At this time, the Fourier transform process can be performed by, for example, software “Digital Micrograph” manufactured by Gatan. It should be noted that other versatile software that can be easily reproduced (implemented) by those skilled in the art may be used for the Fourier transform processing from the lattice image obtained by the HAADF-STEM. Here, the HAADF-STEM image shown in FIG. 5A has a bright part and a dark part. The bright part corresponds to the part where the atomic sequence exists, and the dark part corresponds to the part between the atomic sequence.

Diffraction pattern Next, Fourier transform (FT) processing is performed on a 40 nm square portion (portion surrounded by a broken line) of the lattice image (HAADF-STEM image) shown in FIG. Here, a diffraction pattern (diffraction data) including a plurality of diffraction spots corresponding to a plurality of atomic planes is acquired by performing a Fourier transform process on a range surrounded by a broken line of the acquired lattice image. This Fourier transform processing can be performed by, for example, software “Digital Micrograph” manufactured by Gatan. For the Fourier transform process, other general-purpose software that can be easily reproduced (implemented) by those skilled in the art may be used.

  FIG. 5 (B) is a photograph showing a diffraction pattern obtained by performing a fast Fourier transform (FFT) process on the lattice image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. 5 (A). It is. In the diffraction pattern shown in FIG. 5B, a plurality of diffraction ring portions (diffraction spots) are observed in a ring shape (annular) around the brightest spot that can be seen at the center as the intensity indicating the absolute value.

  In the diffraction pattern shown in FIG. 5 (B), a diffraction ring portion having a width of 0.7 to 1.0 when the distance between Si regular tetrahedrons is 1.0 is determined. Here, the Si tetrahedral distance is equivalent to the distance between the central Si atom of the Si tetrahedral structure and the central Si atom of the adjacent Si regular tetrahedral structure (simply abbreviated as Si-Si distance). To do. Incidentally, this distance corresponds to the surface interval of the Si (220) plane in the Si diamond structure. Therefore, in this step, among the plurality of diffraction ring portions (diffraction spots), the diffraction ring portion corresponding to the Si (220) plane is assigned, and the diffraction ring portion is assigned a distance between Si tetrahedrons of 1. A diffraction ring portion having a width of 0.7 to 1.0 when 0 is set. For the attribution of the diffraction ring portion (diffraction line), for example, a known document (gazette, academic book, etc.) or a document related to various silicon electron diffraction lines published on the Internet can be used. For example, “Technical Report”, Vol. 9, March 2007, I.I. Engineering Department Technical Workshop 8. Acquisition of technology related to electron diffraction pattern observation by transmission electron microscope, Noriyuki Saito, Shigeyasu Arai, Graduate School of Engineering, Faculty of Engineering, Materials / Analysis Technology (http://eng.engg.nagaya-u.ac.jp/gihou) /V9/047.pdf) etc., and can be carried out with reference to literature relating to electron diffraction lines of silicon.

Inverse Fourier transform image Next, the diffraction ring portion existing in a width of 0.7 to 1.0, that is, the Si (220) plane when the distance between the above-mentioned Si tetrahedrons of the diffraction pattern is 1.0. Inverse Fourier transform processing is performed for the corresponding diffraction ring portion. An inverse Fourier transform image is acquired by performing an inverse Fourier transform process on the diffraction ring portion corresponding to the Si (220) plane (extracted figure / extracted data from which data is extracted). The inverse Fourier transform process can be performed by, for example, software “Digital Micrograph” manufactured by Gatan. For the inverse Fourier transform process, other general-purpose software that can be easily reproduced (implemented) by those skilled in the art may be used.

  FIG. 5C shows an inverse Fourier transform image obtained by performing inverse fast Fourier transform processing on the extracted figure from which data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 5B is extracted. It is a photograph which shows. As shown in FIG. 5C, in the obtained inverse Fourier transform image, a light / dark pattern composed of a plurality of bright portions (bright portions) and a plurality of dark portions (dark portions) is observed. Most of the bright and dark portions are amorphous regions (Si amorphous regions) that are irregularly arranged without periodic arrangement. However, as shown in FIG. 5C, regions where the bright portions are periodically arranged (periodic arrangement portions existing in the ellipses surrounded by broken lines in FIG. 5C) are scattered. ing. That is, in the inverse Fourier transform image shown in FIG. 5C, in the amorphous region other than the periodic array portion existing in the ellipse surrounded by the broken line, the bright portion and the dark portion are straight and bent in the middle. They are not stretched into a shape and are not regularly arranged. In addition, there is a portion where the brightness contrast is weak between the bright portion and the dark portion. The bright and dark pattern structure consisting of bright and dark portions in the amorphous region other than the periodic array portion present in the ellipse surrounded by the broken line is that the sample to be observed is amorphous or fine in the amorphous region. It shows that it has a crystal structure.

  Then, in a region (amorphous region) that does not include a periodic array portion existing in an ellipse surrounded by a broken line of the inverse Fourier transform image as shown in FIG. An area of 20 × 20 nm field of view is secured (selected), and the number of bright parts (corresponding to dots = Si regular tetrahedron units) in this field of view is measured. Next, a value obtained by dividing 20 nm, which is the length of one side of the visual field, by the square root of the number of bright portions is defined as a distance between Si regular tetrahedra. For example, if the number of bright portions (corresponding to dots = Si regular tetrahedron unit) in an arbitrary 20 nm square field region is 100, 20 nm ÷ √ (100) = 20 nm / 10 = 2 nm is Si regular tetrahedron. It becomes a distance.

  According to this embodiment, since the value of the distance between Si tetrahedrons is set to 0.38 nm or more, the amorphous region can be made amorphous. As a result, Li ions can be easily inserted and desorbed between the expanded Si-Si during charge and discharge, and the cycle durability of the negative electrode and the electric device using the negative electrode active material of this embodiment is greatly improved. It is something that can be done. In a preferred embodiment of the present invention, the Si tetrahedral distance in the amorphous region is preferably 0.40 nm or more, more preferably 0.44 nm or more, and further preferably 0.47 nm or more. More preferably, it is 0.47 nm or more, and particularly preferably 0.475 nm or more. The upper limit value of the distance between the Si tetrahedrons in the amorphous region is not particularly limited, but can be said to be 0.55 nm or less from a theoretical point of view.

<Silicide phase>
On the other hand, the silicide phase constituting the sea (continuous phase) having the above-described sea-island structure is a crystal phase mainly composed of transition metal silicide (silicide). Since this silicide phase contains a transition metal silicide (eg, TiSi ₂ ), the silicide phase is excellent in affinity with the a-Si phase, and particularly, cracks at the crystal interface due to volume expansion during charging can be suppressed. Furthermore, the silicide phase is superior in terms of electron conductivity and hardness compared to the a-Si phase. Thus, the silicide phase also plays a role of improving the low electron conductivity of the a-Si phase and maintaining the shape of the active material against the stress during expansion. In this embodiment, the silicide phase having such characteristics constitutes the sea (continuous phase) of the sea-island structure, so that the electron conductivity of the negative electrode active material (silicon-containing alloy) can be further improved. Moreover, the stress during expansion of the a-Si phase can be relaxed to prevent cracking of the active material, which is considered to contribute to the improvement of cycle durability.

A plurality of phases may exist in the silicide phase. For example, _two or more phases (for example, MSi ₂ and MSi) having different composition ratios between the transition metal element M and Si may exist. Moreover, two or more phases may exist by including a silicide with different transition metal elements. Here, the type of transition metal (M) contained in the silicide phase is not particularly limited, but is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu, and Fe, and more preferably Ti. Or Zr, particularly preferably Ti. These elements have a higher electron conductivity and higher strength than silicides of other elements when silicides are formed. In particular, TiSi ₂ , which is a kind of silicide when the transition metal element is Ti, is preferable because it exhibits very excellent electronic conductivity. In view of these characteristics of silicide and the excellent identification of amorphous Si described above, the transition metal silicide is preferably TiSi ₂ and the a-Si phase is preferably amorphous.

In particular, when the transition metal element M is Si and there are two or more phases having different composition ratios in the silicide phase (for example, TiSi ₂ and TiSi), the silicide phase is 50 mass% or more, preferably 80 mass% or more, More preferably, 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass is the TiSi ₂ phase.

  The size of the silicide phase is not particularly limited, but in a preferred embodiment, the size of the silicide phase is 50 nm or less, more preferably 30 nm or less, and even more preferably 25 nm or less. With such a configuration, the negative electrode active material (silicon-containing alloy) can have a higher capacity. On the other hand, the lower limit value of the size of the silicide phase is not particularly limited, but from the viewpoint of suppressing expansion / contraction of the a-Si phase accompanying Li insertion / extraction, the diameter of the silicide phase is the diameter of the a-Si phase described above. The absolute value is preferably 10 nm or more, and more preferably 15 nm or more.

Titanium disilicide (TiSi ₂ ) has two types of crystal structures, a C49 structure and a C54 structure. The C49 structure is a phase (metastable phase) exhibiting a high resistivity of about 60 μΩ · cm, and is a bottom-centered orthorhombic structure. On the other hand, the C54 structure is a phase having a low resistivity of about 15 to 20 μΩ · cm (stable phase) and is a face-centered orthorhombic structure. Here, as will be described with reference to FIG. 7A to FIG. 7F in the column of the example described later, disilicide (TiSi ₂ ) contained in the silicide phase of the silicon-containing alloy (negative electrode active material) according to the present embodiment. The crystal structure was confirmed to be C54 structure. Disilicide (TiSi ₂ ) having a C54 structure has a low resistivity and a high hardness compared to those having a C49 structure. Therefore, it is considered that the negative electrode active material according to the present embodiment exhibits high electronic conductivity and is excellent in the effect of relieving the stress caused by the expansion and contraction of the a-Si phase in the active material during charge / discharge. It seemed that it contributed to the realization of cycle durability. From the above, in a preferred embodiment of the present invention, when the transition metal silicide contained in the silicide phase is titanium disilicide (TiSi ₂ ), the main component (TiSi ₂ has a C54 structure) (50 mass% or more by mass ratio). Here, “main component” means that the mass ratio of TiSi ₂ having a C54 structure in 100 mass% of the silicide phase is more than 50 mass%, preferably 80 mass% or more, more preferably It is 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

<Crystal structure analysis of silicon-containing alloys>
In the X-ray diffraction measurement using CuKα1 ray, the silicon-containing alloy that constitutes the negative electrode active material in the present embodiment is 2θ = for the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 °. It is also characterized in that the value (B / A) of the diffraction peak intensity B on the (311) plane of the transition metal silicide in the range of 37 to 45 ° is 1.34 or more (regulation (D)). . The value (B / A) of this ratio is preferably 1.50 or more, more preferably 2.00 or more, and further preferably 2.05 or more. In the present application, the X-ray diffraction measurement for calculating the intensity ratio of the diffraction peaks is performed using the method described in the column of Examples described later.

  Here, the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 ° can be obtained as follows.

  First, in the diffraction spectrum obtained by the X-ray diffraction analysis, a point where the perpendicular and the diffraction spectrum at 2θ = 24 ° intersect is defined as a. Similarly, let b be the point where the perpendicular at 2θ = 33 ° and the X-ray diffraction spectrum intersect. Here, a line segment ab is defined as a base line, and a point at which a perpendicular line at the diffraction peak (2θ = about 28.5 °) of the Si (111) plane intersects the base line is defined as c. Then, the diffraction peak intensity A of the Si (111) plane is obtained as the length of the line segment cd connecting the vertex d and the point c of the diffraction peak (2θ = about 28.5 °) of the Si (111) plane. be able to.

Similarly, the diffraction peak intensity B of the transition metal silicide in the range of 2θ = 37 to 45 ° can be obtained as follows. Hereinafter, the case where the silicide of the transition metal is TiSi ₂ will be described as an example.

First, in the diffraction spectrum obtained by X-ray diffraction analysis, let e be the point where the perpendicular and diffraction spectrum at 2θ = 37 ° intersect. Similarly, let f be the point where the perpendicular at 2θ = 45 ° and the X-ray diffraction spectrum intersect. Here, the line segment ef is the base line, and g is the point where the perpendicular line at the TiSi ₂ diffraction peak (2θ = about 39 °) and the base line intersect. Then, the diffraction peak intensity B of TiSi ₂ can be obtained as the length of the line segment gh connecting the vertex h of the diffraction peak of TiSi ₂ (2θ = about 39 °) and the point g.

In a preferred embodiment, another peak area ratio based on Raman spectroscopy is further defined. That is, the peak area S of the crystalline silicon with a peak at 475cm ^-1 in the Raman spectrum (Cry-Si), and the peak area of amorphous silicon having a peak at ^{420cm -1 S (Amo-Si)} , the peak area ratio S (Amo-Si) / S (Cry-Si) is preferably 1.00 or more (regulation (E)). This value is preferably 1.05 or more, and more preferably 1.10 or more. When the value of the peak area ratio (S (Amo-Si) / S (Cry-Si)) is within such a range, there is an advantage that the cycle durability can be further improved. The value of the peak area ratio (S (Amo-Si) / S (Cry-Si)) can be calculated by the method described in the column of Examples described later.

  In other preferred embodiments, another peak intensity ratio based on X-ray diffraction measurements is further defined. That is, in the X-ray diffraction measurement using the CuKα1 line for the silicon-containing alloy constituting the negative electrode active material, 2θ = 26 to the diffraction peak intensity A on the (111) plane of Si in the range of 2θ = 24 to 33 °. The value (C / A) of the diffraction peak intensity C of the Sn (001) plane in the range of 35 ° is preferably 1.085 or less. This value is more preferably 1.070 or less, and still more preferably 1.060 or less. When the value of the ratio (C / A) is within such a range, there is an advantage that cycle durability can be further improved. The diffraction peak intensity C on the (001) plane of Sn in the range of 2θ = 26 to 35 ° used for calculating the ratio value (C / A) should also be measured by the same method as described above. Can do. That is, in the diffraction spectrum obtained by X-ray diffraction analysis, let i be the point where the perpendicular and the diffraction spectrum at 2θ = 26 ° intersect. Similarly, let j be the point where the perpendicular at 2θ = 35 ° and the X-ray diffraction spectrum intersect. Here, a line segment ij is a base line, and a point at which a perpendicular line at the diffraction peak (2θ = about 30.6 °) of the Sn (001) plane intersects the base line is k. Then, the diffraction peak intensity C of the (001) plane of Sn is obtained as the length of the line segment kl connecting the vertex l of the diffraction peak (2θ = about 30.6 °) of the Sn (001) plane and the point k. be able to.

  In addition, about the prescription | regulation (A) mentioned above, it can control to satisfy | fill the said prescription | regulation (A) by adjusting the composition of the raw material used when manufacturing a silicon containing alloy. Moreover, although there is no restriction | limiting in particular about the control means for satisfy | filling prescription | regulation (B)-(F), For example, the manufacturing method which concerns on the other form of this invention mentioned later is employ | adopted, or a transition metal (for example, When the blending amount of Ti) is constant, the regulation (B) to (F) can be controlled by setting the Sn blending amount relatively small.

  Although the particle diameter of the silicon-containing alloy constituting the negative electrode active material in the present embodiment is not particularly limited, the average particle diameter is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm.

(Method for producing negative electrode active material)
There is no particular limitation on the method for producing the negative electrode active material for an electrical device according to the present embodiment, and conventionally known knowledge can be referred to as appropriate. However, the present application has a structure in which the a-Si phase is dispersed in the silicide phase. In addition, as an example of a method for producing a negative electrode active material made of a silicon-containing alloy whose Si tetrahedral distance and silicide / Si peak intensity ratio (B / A) are values within a predetermined range, A manufacturing method utilizing mechanical alloying is provided. That is, according to another embodiment of the present invention, there is provided a method for producing a negative electrode active material for an electrical device comprising a silicon-containing alloy having the composition represented by the chemical formula (I), wherein the composition is the same as that of the silicon-containing alloy. The negative electrode active material for an electrical device made of the silicon-containing alloy is obtained by subjecting the mother alloy powder having a mechanical alloying treatment to a powder that has a centrifugal force of 20 [G] or more. A method for producing a negative electrode active material for an electrical device is also provided. In this way, a negative alloy active material (silicon-containing alloy) is manufactured by performing a mechanical alloying process using a ball mill apparatus to which a relatively large centrifugal force is applied, thereby manufacturing an alloy having the above-described microstructure. It becomes possible to do. In addition, the distance between Si tetrahedrons in the obtained alloy can be further increased, and the value of the silicide / Si peak intensity ratio can be controlled to a value within the predetermined range. A production method that can effectively contribute to the improvement of the cycle durability of the substance is provided. Hereinafter, the manufacturing method according to the present embodiment will be described in more detail.

  First, in order to obtain a master alloy, high-purity raw material powders are prepared for each of silicon (Si), tin (Sn), and a transition metal (for example, titanium (Ti)) as raw materials.

  Subsequently, a mechanical alloying process is performed using the raw material powder prepared above.

  Since the alloying process is performed by mechanical alloying, the phase state can be easily controlled. Therefore, the mechanical alloying process uses a ball mill device to pulverize balls and alloy raw material powder into a pulverizing pot. Alloying can be achieved by applying energy by applying. That is, heat is generated by applying energy, and the raw material powder is alloyed to amorphize the a-Si phase, solid solution of tin in the phase, and formation of a silicide phase.

  The manufacturing method according to this embodiment is characterized in that the centrifugal force applied to the contents by the ball mill device used for the mechanical alloying process is 20 [G] or more. Silicon-containing alloy (negative electrode active material) that can exhibit equivalent or higher cycle durability even in shorter time processing by performing mechanical alloying using a ball mill device that applies a relatively large centrifugal force. Can be manufactured. In addition, since the amount of Sn, which is a relatively expensive raw material, can be reduced, the manufacturing cost of the silicon-containing alloy (negative electrode active material) can also be reduced. The value of the centrifugal force is preferably 50 [G] or more, more preferably 100 [G] or more, still more preferably 120 [G] or more, and particularly preferably 150 [G] or more. Yes, most preferably 175 [G] or more. On the other hand, the upper limit value of the centrifugal force is not particularly limited, but normally about 200 [G] is realistic.

  Here, the value of the centrifugal force applied to the contents in the ball mill device is calculated by the following mathematical formula:

  In the above formula, Gnl is the centrifugal force [G], rs is the revolution radius [m], rpl is the rotation radius [m], iw is the rotation / revolution ratio [−], and rpm is the rotation speed [times / minute]. Therefore, it can be seen that the centrifugal force Gnl increases as the revolution radius rs increases, the rotation radius rpl decreases, and the rotation speed increases.

  The specific configuration of the ball mill apparatus is not particularly limited, and conventionally known ball mill apparatuses such as a planetary ball mill apparatus and a stirring ball mill apparatus can be used as long as the above-described centrifugal force is satisfied. However, in the manufacturing method according to this embodiment, a stirring ball mill device is preferably used. The stirring ball mill device includes a container having a cylindrical inner surface and a stirring blade provided in the container. In the container of this stirring ball mill apparatus, raw material powder, balls, a solvent and a processing agent are charged. Unlike the planetary ball mill apparatus, the stirring blade provided in the container rotates to alloy the raw material powder without rotating the container. When such a stirring ball mill apparatus is used, the contents of the container can be vigorously stirred by the stirring blades, so that a centrifugal force larger than that of other ball mill apparatuses can be applied to the contents of the container.

  Thus, by increasing the value of the centrifugal force of the apparatus used in the mechanical alloying process (alloying process), the distance between the Si tetrahedrons in the amorphous region can be increased. Further, the value of the silicide / Si peak intensity ratio (B / A) can be within the predetermined range.

  In general, as the time for performing the mechanical alloying process is increased, a silicon-containing alloy having a suitable microstructure can be obtained. However, in the manufacturing method according to this embodiment, a relatively large centrifugal force is used as described above. Since the mechanical alloying process is performed so that force is applied to the contents, even if the mechanical alloying process time is shortened, it is possible to achieve the same or higher cycle durability. From such a viewpoint, in the manufacturing method according to this embodiment, the mechanical alloying treatment time is preferably 45 hours or less, more preferably 40 hours or less, still more preferably 36 hours or less, and even more preferably. Is 30 hours or less, particularly preferably 24 hours or less, and most preferably 20 hours or less. In addition, although the lower limit of the time of a mechanical alloying process is not set in particular, it may usually be 12 hours or more.

  In the mechanical alloying process using a ball mill apparatus, a raw material powder can be alloyed using a conventionally known ball. Preferably, the ball is 1 mm or less, particularly 0.1 to 1 mm. A titanium or zirconia having a diameter is used. In particular, in this embodiment, a titanium ball manufactured by the plasma rotating electrode method is preferably used. A titanium or zirconia ball having a diameter of 1 mm or less manufactured by such a plasma rotating electrode method has a uniform spherical shape, and is particularly preferable as a ball for obtaining a silicon-containing alloy.

  In the present embodiment, the solvent charged in the container of the stirring ball mill is not particularly limited. Examples of such a solvent include water (particularly ion-exchanged water), methanol, ethanol, propanol, butanol, pentanol, dimethyl ketone, diethyl ketone, diethyl ether, dimethyl ether, diphenyl ether, toluene, and xylene. These solvents are used alone or in appropriate combination.

  Furthermore, in the present invention, the treatment agent charged in the container is not particularly limited. Examples of such a treating agent include a surfactant and / or a fatty acid in addition to carbon powder for preventing the contents from adhering to the inner wall of the container.

  The mechanical alloying process by the above-described method is usually performed in a dry atmosphere, but the particle size distribution after the mechanical alloying process may have a very large or small width. For this reason, it is preferable to perform the grinding | pulverization process and / or classification process for adjusting a particle size.

As described above, the predetermined alloy included in the negative electrode active material layer has been described, but the negative electrode active material layer may contain other negative electrode active materials. Examples of the negative electrode active material other than the predetermined alloy include natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, carbon such as hard carbon, pure metal such as Si and Sn, and the predetermined composition. Alloy-based active material out of ratio, or metal oxide such as TiO, Ti ₂ O ₃ , TiO ₂ , SiO ₂ , SiO, SnO ₂ , lithium such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN And transition metal composite oxides (composite nitrides), Li—Pb alloys, Li—Al alloys, Li, and the like. However, from the viewpoint of sufficiently exerting the effects exhibited by using the predetermined alloy as the negative electrode active material, the content of the predetermined alloy in the total amount of 100% by mass of the negative electrode active material is preferably It is 50-100 mass%, More preferably, it is 80-100 mass%, More preferably, it is 90-100 mass%, Especially preferably, it is 95-100 mass%, Most preferably, it is 100 mass%.

  Subsequently, the negative electrode active material layer 13 includes a binder.

(Binder)
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. There is no restriction | limiting in particular also about the kind of binder used for a negative electrode active material layer, What was mentioned above as a binder used for a positive electrode active material layer can be used similarly. Therefore, detailed description is omitted here.

  The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to It is 20 mass%, More preferably, it is 1-15 mass%.

(Requirements common to the positive and negative electrode active material layers 15 and 13)
The requirements common to the positive and negative electrode active material layers 15 and 13 will be described below.

  The positive electrode active material layer 15 and the negative electrode active material layer 13 include a conductive additive, an electrolyte salt (lithium salt), an ion conductive polymer, and the like as necessary. In particular, the negative electrode active material layer 13 essentially includes a conductive additive.

Conductive auxiliary agent A conductive auxiliary agent means the additive mix | blended in order to improve the electroconductivity of a positive electrode active material layer or a negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  The content of the conductive additive mixed into the active material layer is in the range of 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more with respect to the total amount of the active material layer. In addition, the content of the conductive additive mixed in the active material layer is 15% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less with respect to the total amount of the active material layer. is there. By defining the compounding ratio (content) of the conductive aid in the active material layer within the above range, the electronic conductivity of the active material itself is low and the electrode resistance can be reduced by the amount of the conductive aid. The That is, it is possible to sufficiently ensure the electronic conductivity without hindering the electrode reaction, to suppress the decrease in the energy density due to the decrease in the electrode density, and to improve the energy density due to the increase in the electrode density. .

  Moreover, the conductive binder having the functions of the conductive assistant and the binder may be used in place of the conductive assistant and the binder, or may be used in combination with one or both of the conductive assistant and the binder. . As the conductive binder, commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used.

Electrolyte salt (lithium salt)
Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

Ion conductive polymer Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The mixing ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous solvent secondary battery.

  There is no particular limitation on the thickness of each active material layer (active material layer on one side of the current collector), and conventionally known knowledge about the battery can be referred to as appropriate. For example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm in consideration of the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

<Current collector>
The current collectors 11 and 12 are made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

  There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

  The shape of the current collector is not particularly limited. In the laminated battery 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (such as an expanded grid) can be used.

  In the case where the negative electrode active material is formed directly on the negative electrode current collector 12 by sputtering or the like, it is desirable to use a current collector foil.

  There is no particular limitation on the material constituting the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be employed.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material by sputtering to the current collector.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin.

  The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. Moreover, there is no restriction | limiting in particular as electroconductive carbon. Preferably, it includes at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

  The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

<Electrolyte layer>
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

  The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Examples include carbonates such as methylpropyl carbonate (MPC).

As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 SO 3 , etc. A compound that can be added to the active material layer of the electrode can be employed.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the liquid electrolyte (electrolytic solution) is injected into a matrix polymer made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block ion conduction between the layers.

  Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  The ratio of the liquid electrolyte (electrolytic solution) in the gel electrolyte is not particularly limited, but is preferably about several mass% to 98 mass% from the viewpoint of ionic conductivity. In the present embodiment, the gel electrolyte having a large amount of electrolytic solution having a ratio of the electrolytic solution of 70% by mass or more is particularly effective.

  In the case where the electrolyte layer is composed of a liquid electrolyte, a gel electrolyte, or an intrinsic polymer electrolyte, a separator may be used for the electrolyte layer. Specific examples of the separator (including non-woven fabric) include a microporous film made of polyolefin such as polyethylene and polypropylene, a porous flat plate, and a non-woven fabric.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

<Current collector plate and lead>
A current collecting plate may be used for the purpose of taking out the current outside the battery. The current collector plate is electrically connected to the current collector and the lead, and is taken out of the laminate sheet that is a battery exterior material.

  The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum is more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Copper or the like is preferable. Note that the same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

  The positive terminal lead and the negative terminal lead are also used as necessary. As the material of the positive terminal lead and the negative terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. It should be noted that the part taken out from the battery outer packaging material 29 has a heat insulating property so as not to affect the product (for example, automobile parts, particularly electronic devices) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

<Battery exterior material>
As the battery exterior material 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV.

  In addition, said lithium ion secondary battery can be manufactured with a conventionally well-known manufacturing method.

<Appearance structure of lithium ion secondary battery>
FIG. 2 is a perspective view showing the appearance of a stacked flat lithium ion secondary battery.

  As shown in FIG. 2, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive current collector 59 for taking out power from both sides thereof, a negative current collector, and the like. The electric plate 58 is pulled out. The power generation element 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50 and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode current collector plate 59 and the negative electrode current collector plate 58 to the outside. Sealed. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery (stacked battery) 10 shown in FIG. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 including a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

  The lithium ion secondary battery is not limited to a laminated flat shape (laminate cell). In a wound type lithium ion battery, a cylindrical shape (coin cell), a prismatic shape (square cell), or such a cylindrical shape deformed into a rectangular flat shape Further, it may be a cylindrical cell, and is not particularly limited. The cylindrical or prismatic shape is not particularly limited, for example, a laminate film or a conventional cylindrical can (metal can) may be used as the exterior material. Preferably, the power generation element is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Further, the removal of the positive electrode current collector plate 59 and the negative electrode current collector plate 58 shown in FIG. 2 is not particularly limited. The positive electrode current collector plate 59 and the negative electrode current collector plate 58 may be drawn out from the same side, or the positive electrode current collector plate 59 and the negative electrode current collector plate 58 may be divided into a plurality of parts and taken out from each side. It is not limited to the one shown in FIG. Further, in a wound type lithium ion battery, instead of the current collector plate, for example, a terminal may be formed using a cylindrical can (metal can).

  As described above, the negative electrode and the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment are large vehicles such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles. It can be suitably used as a capacity power source. That is, it can be suitably used for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density.

  In the above embodiment, the lithium ion battery is exemplified as the electric device. However, the present invention is not limited to this, and can be applied to other types of secondary batteries and further to primary batteries. Moreover, it can be applied not only to batteries but also to capacitors.

  The invention is explained in more detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples.

Example 1
[Manufacture of silicon-containing alloys]
A silicon-containing alloy having a composition of Si ₆₀ Sn ₁₀ Ti ₃₀ (composition ratio is mass ratio) was manufactured by the following method.

  Specifically, 1620 g of zirconia pulverized balls (φ5 mm) and 1 g of carbon (SGL) were charged into a SUS pulverizing pot using a stirring ball mill device C-01M manufactured by ZOZ, Germany, and then at 1000 rpm for 10 minutes. A pre-grinding process was performed. Thereafter, 100 g of each raw material powder of each alloy is charged, alloyed at 1500 rpm for 20 hours (alloying treatment), and then finely pulverized at 400 rpm for 1 hour to obtain a silicon-containing alloy (negative electrode active material). Got. In the stirring ball mill apparatus used in this example, the revolution radius rs = 0.070 [m], the rotation radius rpl = 0 [m], and the rotation speed rpm = 1500 [times / minute]. The force Gnl was calculated to be 176.0 [G]. Moreover, the average particle diameter (D50) of the obtained silicon-containing alloy (negative electrode active material) powder was 7.84 μm.

[Production of negative electrode]
80 parts by mass of the silicon-containing alloy (Si ₆₀ Sn ₁₀ Ti ₃₀ ) produced above as a negative electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, and 15 parts by mass of polyimide as a binder, A negative electrode slurry was obtained by dispersing in N-methylpyrrolidone using a defoaming kneader (Thinky AR-100). Next, the obtained negative electrode slurry was uniformly applied to both surfaces of a negative electrode current collector made of copper foil so that the thickness of the negative electrode active material layer was 30 μm, and dried in a vacuum for 24 hours. Obtained.

[Production of lithium ion secondary battery (coin cell)]
The negative electrode produced above and the counter electrode Li were opposed to each other, and a separator (polyolefin, film thickness 20 μm) was disposed therebetween. Next, a laminate of a negative electrode, a separator, and a counter electrode Li was disposed on the bottom side of a coin cell (CR2032, material: stainless steel (SUS316)). Furthermore, in order to maintain the insulation between the positive electrode and the negative electrode, a gasket is attached, the following electrolyte is injected with a syringe, the spring and spacer are stacked, the upper side of the coin cell is overlapped and sealed by caulking. A lithium ion secondary battery (coin cell) was obtained.

In addition, as said electrolyte solution, hexafluorophosphoric acid which is lithium salt in the organic solvent which mixed ethylene carbonate (EC) and diethyl carbonate (DEC) in the ratio of EC: DEC = 1: 2 (volume ratio). lithium (LiPF ₆₎ was used dissolved at a concentration of 1 mol / L.

(Example 2)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 1 except that the composition of the silicon-containing alloy was changed to Si _62.5 Sn _7.5 Ti _30. did. In addition, the average particle diameter (D50) of the obtained silicon-containing alloy (negative electrode active material) powder was 4.47 μm.

(Example 3)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 1 except that the composition of the silicon-containing alloy was changed to Si ₆₅ Sn ₅ Ti ₃₀ . In addition, the average particle diameter (D50) of the obtained silicon-containing alloy (negative electrode active material) powder was 6.43 μm.

Example 4
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 1 except that the composition of the silicon-containing alloy was changed to Si _67.5 Sn _2.5 Ti _30. did. In addition, the average particle diameter (D50) of the obtained silicon-containing alloy (negative electrode active material) powder was 3.22 μm.

(Example 5)
Using high-purity metal Si ingot (5N), high-purity Ti wire (3N), high-purity Sn plate (3N) and arc melting method, Si alloy (Si 60 mass%, Sn10 mass%, Ti3 mass%) An ingot was produced.

Subsequently, using the ingot obtained above as a mother alloy, a silicon-containing alloy was produced by a liquid rapid solidification method. Specifically, using a liquid rapid solidification apparatus NEV-A05 type manufactured by Nisshin Giken Co., Ltd., Si ₆₀ Sn was placed in a quartz nozzle installed in a chamber reduced to a gauge pressure of -0.03 MPa after Ar substitution. _{A 10} Ti ₃₀ ingot (mother alloy) is charged and melted by high frequency induction heating, and then injected onto a Cu roll having a rotation speed of 4000 rpm (peripheral speed: 41.9 m / sec) at an injection pressure of 0.05 MPa. A ribbon-shaped alloy (quenched ribbon) was prepared.

  Thereafter, the ribbon-like alloy (quenched ribbon) obtained above was pulverized to a size of about 15 μm in diameter, and the obtained pulverized product was subjected to mechanical alloying treatment. Specifically, using a planetary ball mill device P-6 manufactured by Fricht, Germany, the zirconia pulverized balls and the above pulverized product were put into a zirconia pulverized pot and subjected to mechanical alloying at 600 rpm for 48 hours. Alloyed. Thereafter, a pulverization treatment was performed at 400 rpm for 1 hour to obtain a silicon-containing alloy (negative electrode active material). In the planetary ball mill apparatus used in this example, the revolution radius rs = 0.060 [m], the revolution radius rpl = 0.033 [m], the revolution-revolution ratio iw = −1.818 [−], and the rotation speed Since rpm = 600 [times / min], the centrifugal force Gnl = 19.4 [G] was calculated. Moreover, the average particle diameter (D50) of the obtained silicon-containing alloy (negative electrode active material) powder was 1.12 μm.

(Comparative example)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 except that the composition of the silicon-containing alloy was changed to Si ₆₀ Sn ₂₀ Ti ₂₀ . In addition, the average particle diameter (D50) of the obtained silicon-containing alloy (negative electrode active material) powder was 10.39 μm.

[Analysis of the structure of the anode active material]
The structure of the negative electrode active material (silicon-containing alloy) produced in Example 1 was analyzed.

FIG. 3A shows an EDX (energy dispersive X-ray) of an observation image (low magnification) of the negative electrode active material (silicon-containing alloy) of Example 1 observed with a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). It is the image which performed element intensity mapping by the spectroscopy method. On the other hand, FIG. 3 (B) is a photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of Example 1 shown in FIG. 3 (A). From the result shown in FIG. 3 (A), it was considered that a silicide (TiSi ₂ ) phase was present at a site where Ti was present because Si was also present. It was also found that Si was present at sites where Ti was not present, and that Sn was present at sites where Ti was not present and Ti was present. Furthermore, in the observation image shown in FIG. 3B, a regular diffraction pattern can be seen in the diffraction pattern obtained by fast Fourier transform of an image of a portion considered to contain a silicide (TiSi ₂ ) phase. (Existence of crystal structure). Further, in the EDX spectrum obtained for the same part, Si and Ti were present at an atomic ratio of about 2: 1, so that the part was confirmed to be a silicide (TiSi ₂ ) phase.

  Further, in the observation image shown in FIG. 3B, a regular diffraction pattern was not seen in the diffraction pattern obtained by fast Fourier transform of the image of the portion where Si was not present and Ti was present. Moreover, since E was present as a main component in the EDX spectrum obtained for the same part, it was confirmed that the part was an a-Si phase. In this EDX spectrum, it was also confirmed that Sn was contained in the a-Si phase. Since Sn does not form silicide with Si, it is considered that Sn is dissolved in the a-Si phase. It was.

  Similarly to the above, for the images (low magnification) observed by HAADF-STEM of the silicon-containing alloys of Examples 3 to 5 and the comparative example, images obtained by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy), respectively. Shown in FIGS. The alloys of Examples 3 to 5 shown in FIGS. 4A to 4C had the same microstructure as the alloy of Example 1 described above with reference to FIG. From the results shown in FIG. 3 and FIG. 4, it can be seen that in the alloy of the comparative example, Sn does not dissolve in the a-Si phase so much, and most of it is unevenly distributed as a phase of Sn alone. On the other hand, in the alloys of the examples, Sn was not unevenly distributed, and it was also found that most of Sn was dissolved in the a-Si phase.

Next, FIG. 5A is an observation image (high magnification) by HAADF-STEM of the negative electrode active material (silicon-containing alloy) of Example 1 which is the same as FIG. 3B. FIG. 5B shows a diffraction pattern obtained by performing a fast Fourier transform (FFT) process on the observation image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. 5A. It is a photograph shown. FIG. 5C shows an inverse Fourier transform obtained by performing inverse fast Fourier transform processing on the extracted figure from which data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 5B is extracted. It is a photograph which shows a conversion image. Similarly, FIGS. 6A and 6B show the following photographs:
6A (A): Photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of Example 3 shown in FIG. 4 (A). Inverse Fourier transform image of Example 3 obtained from the observed image of FIG. 6A (A) FIG. 6A (C): Surrounded by the square of the HAADF-STEM observed image (low magnification) of Example 4 shown in FIG. 6A (D): Inverse Fourier transform image of Example 4 obtained from the observation image of FIG. 6A (C) FIG. 6B (E): FIG. 4 (C) 6B (F): Obtained from the observation image of FIG. 6B (E). FIG. 6B (F): The observation image (high magnification) of the HAADF-STEM observation image (low magnification) of Example 5 shown in FIG. Inverse Fourier transform image of Example 5 obtained FIG. 6B (G): ratio shown in FIG. 4 (D) A photograph showing an observation image (high magnification) obtained by enlarging a portion surrounded by a square of the HAADF-STEM observation image (low magnification) of the example. FIG. 6B (H): of the comparative example obtained from the observation image of FIG. 6B (G) Inverse Fourier transform image.

Summarizing the above results, the negative electrode active materials (silicon-containing alloys) obtained in Examples 1 and 3 to 5 are amorphous or low crystalline in which Sn is dissolved in the crystal structure of Si. It has been found that the a-Si phase containing Si has a structure in which it is dispersed in a silicide (TiSi ₂ ) phase mainly composed of a transition metal silicide. Although the results are not shown, it has been confirmed that the negative electrode active material (silicon-containing alloy) obtained in Example 2 has a similar structure.

On the other hand, in the negative electrode active material (silicon-containing alloy) of the comparative example, a structure similar to that of the example is not confirmed, and on the contrary, a structure in which a silicide (TiSi ₂ ) phase is dispersed in an a-Si phase. confirmed.

[Measurement of Si Tetrahedral Distance (Si-Si Distance) of Amorphous Region of Negative Electrode Active Material]
About the negative electrode active material (silicon-containing alloy) produced in each of Examples 1, 3 to 5 and Comparative Example, an inverse Fourier transform image (FIG. 5C) obtained by image analysis using a HAADF-STEM observation image. FIG. 6A (B), FIG. 6A (D), FIG. 6B (F) and FIG. 6B (H)) show the results of measuring (calculating) the distance between the Si tetrahedrons of the amorphous region (a-Si phase). It is shown in Table 1 below.

[Analysis of crystal structure of negative electrode active material by X-ray diffraction measurement]
The crystal structure of the negative electrode active material (silicon-containing alloy) produced in each of Examples 1 to 5 and Comparative Example was analyzed by an X-ray diffraction measurement method. The apparatus and conditions used for the X-ray diffraction measurement method are as follows. This X-ray diffraction measurement also confirmed that all Ti contained in the silicon-containing alloy was present as a silicide (TiSi ₂ ) phase.

Device name: X-ray diffractometer (SmartLab9kW) manufactured by Rigaku Corporation
Voltage / Current: 45kV / 200mA
X-ray wavelength: CuKα1
And the diffraction peak of the (111) plane of Si in the range of 2θ = 24 to 33 ° obtained from the X-ray diffraction spectra obtained for the negative electrode active materials (silicon-containing alloys) of Examples 1 to 5 and Comparative Example. From the value of intensity A and the value of diffraction peak intensity B of TiSi ₂ in the range of 2θ = 37 to 45 °, the value of these ratios (SiM / Si peak intensity ratio; B / A) was calculated. The results are shown in Table 1 below.

  Similarly, diffraction of (111) plane of Si in the range of 2θ = 24 to 33 ° obtained from the X-ray diffraction spectra obtained for the negative electrode active materials (silicon-containing alloys) of Examples 1 to 5 and Comparative Example. The value of these ratios (Sn / Si peak intensity ratio; C / A) was calculated from the value of the diffraction peak intensity D of the (001) plane of Sn in the range of 2θ = 26 to 35 ° with respect to the peak intensity A. The results are shown in Table 1 below.

[Analysis of crystal structure of negative electrode active material by Raman spectroscopy]
The structure of the negative electrode active material (silicon-containing alloy) produced in each of Examples 1 to 5 and Comparative Example was analyzed by Raman spectroscopy using the following method.

<Measurement conditions and equipment>
First, for measurement of the Raman spectrum, a negative electrode active material (silicon-containing alloy) powder as a sample was developed on a flat plate. The measurement was performed for each sample by 4 points, and the obtained Raman spectra were averaged. The measurement conditions were a 20 × objective lens, a semiconductor laser with an excitation wavelength of 532 nm used as incident light, a measurement range of 60 to 1550 cm ⁻¹ , a measurement time of 30 seconds, and an integration count of 2 times. Here, the equipment used is as follows.
Device name: Bruker Optics Microscopic Laser Raman SENTERRA
<Curve fitting>
Curve fitting was performed based on the data obtained by the Raman spectrum measurement. Curve fitting was performed based on Lorentz functions centered at five positions of 860 cm ⁻¹ , 765 cm ⁻¹ , 475 cm ⁻¹ , 420 cm ⁻¹ , and 315 cm ⁻¹ . Of these, the peak area S (Cry-Si) was calculated by assigning the peak at 475 cm ⁻¹ to that of crystalline silicon. On the other hand, the peak area S (Amo-Si) was calculated by assigning the peak at 420 cm ⁻¹ to that of amorphous silicon. And peak area ratio S (Amo-Si) / S (Cry-Si) was calculated | required from these values. The results are shown in Table 1 below.

[Evaluation of cycle durability]
For each lithium ion secondary battery (coin cell) produced in each of Examples 1 to 4 and Comparative Example, cycle durability was evaluated according to the following charge / discharge test conditions.

(Charge / discharge test conditions)
1) Charge / discharge tester: HJ0501SM8A (Hokuto Denko Co., Ltd.)
2) Charging / discharging conditions [charging process] 0.3C, 2V → 10mV (constant current / constant voltage mode)
[Discharge process] 0.3C, 10mV → 2V (constant current mode)
3) Thermostatic bath: PFU-3K (Espec Corp.)
4) Evaluation temperature: 300K (27 ° C.).

  The evaluation cell is set to the constant current / constant voltage mode in the charging process (referring to the Li insertion process to the evaluation electrode) in the thermostat set to the above evaluation temperature using a charge / discharge tester. The battery was charged from 2 V to 10 mV at 0.1 mA. Thereafter, in the discharge process (referring to the Li desorption process from the electrode for evaluation), a constant current mode was set and discharge was performed from 0.3 C, 10 mV to 2 V. The charge / discharge test was conducted from the initial cycle (1 cycle) to 100 cycles under the same charge / discharge conditions with the above charge / discharge cycle as one cycle. The results of determining the ratio of the discharge capacity at the 50th cycle, the 70th cycle and the 100th cycle (discharge capacity retention rate [%]) to the discharge capacity at the first cycle are shown in Table 1 below.

From the results shown in Table 1, the lithium ion battery using the negative electrode active material according to the present invention is maintained at a high discharge capacity maintenance rate after 50 cycles / 70 cycles, and has excellent cycle durability. I know that there is. In this way, high cycle durability can be realized because the silicon-containing alloy constituting the negative electrode active material is represented by Si—Sn—M (M is one or more transition metal elements). An a-Si phase containing amorphous or low crystalline silicon in which tin is dissolved in the crystal structure of silicon, and having a transition metal silicide as a main component. This is because it has a structure in which the particles are dispersed. Thus, when the silicide phase constitutes a sea (continuous phase) having a sea-island structure, the electronic conductivity of the negative electrode active material (silicon-containing alloy) can be further improved, and the a-Si phase is expanded. It is possible to relax the stress of the active material and prevent the active material from cracking. Further, when tin dissolves in the a-Si phase, the distance between the Si tetrahedrons of the amorphous region (a-Si phase) becomes a value equal to or greater than a predetermined value, so that lithium ions are inserted during charging and discharging.・ It is thought that the elimination reaction is likely to proceed. Furthermore, when the SiM / Si peak intensity ratio (B / A) is a value equal to or greater than a predetermined value, the amorphous-crystal phase transition (to Li ₁₅ Si ₄₎ when Si and Li are alloyed during charging. It is considered that this leads to relaxation of the expansion of the active material particles during charging / discharging while suppressing crystallization of the active material particles. As a result of the silicon-containing alloy constituting the negative electrode active material according to the present invention having a predetermined microstructure, it is considered that the cycle durability is improved as a combined effect of these.

In addition, the observation image (HAADF-STEM image) which observed the fine structure of Examples 1, 3-5, and the negative electrode active material (silicon-containing alloy) of a comparative example with HAADF-STEM, and its enlarged image are FIG. Example 1), FIG. 7B (Example 3), FIG. 7C (Example 4), FIG. 7D (Example 5), and FIG. 7E (Comparative Example) are shown again. Then, it is shown in black portion (a-Si phase) and gray portions (silicide (TiSi ₂₎ phase) region to be respectively diffraction pattern obtained by fast Fourier transform in Figure in each of the enlarged image. Moreover, the XRD chart about each negative electrode active material (silicon-containing alloy) is shown in FIG. 7F. From the diffraction pattern and XRD chart shown in each figure, it is confirmed that the crystal structure of disilicide (TiSi ₂ ) contained in the negative electrode active materials (silicon-containing alloys) of Examples 1, 3 to 5 and Comparative Example is a C54 structure. It was done. Since disilicide (TiSi ₂ ) having a C54 structure has a low resistivity and a high hardness compared to those having a C49 structure, it exhibits high electronic conductivity when used as a negative electrode active material. It is thought that it is excellent in the effect which relieve | moderates the stress which arises by the expansion-contraction of the a-Si phase in the active material at the time of charging / discharging, and this also seems to have contributed to realization of high cycle durability.

10, 50 Lithium ion secondary battery (stacked battery),
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 electrolyte layer,
19 cell layer,
21, 57 power generation element,
25, 58 negative electrode current collector plate,
27, 59 positive current collector,
29, 52 Battery exterior material (laminate film).

Claims (9)

A negative electrode active material for electrical devices, comprising a silicon-containing alloy that satisfies the following requirements (A) to (D):
(A) The following chemical formula (I):
(In the above chemical formula (I),
A is an inevitable impurity,
M is one or more transition metal elements,
x, y, z, and a represent mass% values, where 0 <x <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100. )
Having a composition represented by:
(B) The a-Si phase containing amorphous or low crystalline silicon in which tin is dissolved in the silicon crystal structure is dispersed in a silicide phase mainly composed of a transition metal silicide. Having a structure of
(C) The Si tetrahedral distance by TEM-MRO analysis for the a-Si phase is 0.38 nm or more;
(D) In the X-ray diffraction measurement using CuKα1 line, the transition metal silicide in the range of 2θ = 37 to 45 ° with respect to the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 ° The value (B / A) of the diffraction peak intensity B of the (311) plane is 1.34 or more. The negative electrode active material for an electric device according to claim 1, wherein the silicon-containing alloy further satisfies the following (E):
(E) and the peak area of crystalline silicon having a peak at 475cm ^-1 in the Raman spectrum S (Cry-Si), and the peak area of amorphous silicon having a peak at ^{420cm -1 S (Amo-Si)} , the peak area ratio of S (Amo-Si) / S (Cry-Si) is 1.00 or more. The negative electrode active material for an electric device according to claim 1 or 2, wherein the silicon-containing alloy further satisfies the following (F):
(F) In X-ray diffraction measurement using CuKα1 line, Sn in the range of 2θ = 26 to 35 ° with respect to the diffraction peak intensity A of (111) plane of Si in the range of 2θ = 24 to 33 ° (001) The value (C / A) of the diffraction peak intensity C of the surface is 1.085 or less. The silicide of a transition metal is TiSi _2, and the a-Si phase is amorphous, the negative electrode active material for an electric device according to any one of claims 1 to 3. The negative electrode active material for an electric device according to claim 4, wherein the TiSi ₂ is mainly composed of a material having a C54 structure. The following chemical formula (I):
(In the above chemical formula (I),
A is an inevitable impurity,
M is one or more transition metal elements,
x, y, z, and a represent mass% values, where 0 <x <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100. )
A method for producing a negative electrode active material for an electrical device comprising a silicon-containing alloy having a composition represented by:
The master alloy powder having the same composition as the silicon-containing alloy is subjected to mechanical alloying using a ball mill apparatus in which a centrifugal force of 20 [G] or more is applied, thereby comprising the silicon-containing alloy. The manufacturing method of the negative electrode active material for electric devices which obtains the negative electrode active material for electric devices.   The manufacturing method of the negative electrode active material for electrical devices of Claim 6 whose time of a mechanical alloying process is 45 hours or less.   The negative electrode for electric devices which uses the negative electrode active material for electric devices of any one of Claims 1-5.   An electric device comprising the negative electrode for an electric device according to claim 8.